1. Field of the Invention
The invention relates to a stability control system for an automotive vehicle.
2. Description of the Related Art
In recent years, there is a strong tendency to control stability of an automotive vehicle by controlling braking force applied to four wheels independently. Braking force is applied to one or more wheels so as to gain actually a target yaw rate or a target slip angle of the vehicle given as a target stability parameter based on a steering angle, a vehicle speed, and a yaw rate and a lateral acceleration of the vehicle. This kind of system of driving stability control is known from, for example, Japanese Unexamined Patent Publication No. 2-151571. The system of driving stability control attracts a great deal of attention as a potential safety technique because of its capability of preventing an occurrence of understeering and/or spinning within a limit of tire gripping or adhesion force.
The system of driving stability control of this kind applies braking force to some of the four wheels to cause a yaw moment in the vehicle independently of braking the vehicle. That is, braking force applied to a specific wheel or wheels through the stability control while the vehicle spins or when the slip angle of the vehicle is large bears no direct relation to braking the vehicle. On the other hand, if the driver steps on a brake pedal with the intention of avoiding spin or bringing a spin to the end during execution of the stability control, a confrontation occurs between demands for braking the vehicle and making the vehicle run stably. If either must take preference, measures have to be taken to prevent an occurrence of confrontation between the two demands. Applying braking force simply distributed among the wheels during an occurrence of spin might encourage the spin.